Control mechanism for honing machines



A. M. JOHNSON CONTROL MECHANISM FOR HONING MACHINES Aug. 23, 1949.

Filed Dec. 4, 1944 3 Sheets-Sheet l llllllllllll lllill ll H Illllllllllll Aug. 23, 1949. A. M. JOHNSON CONTROL MECHANISM FOR HONING MACHINES Filed Dec. 4, 1944 3 SheetsSheet 2 wmnmaw a///% aq/bzff kf yoms @149. f?

JAM/4.4. 424% (Arrow-S 23, 1949- A. M. JOHNSON 2,479,622

CONTROL MECHANISM FOR HONING MACHINES Filed Dec. 4, 1944 3 Sheets-Sheet 5 XXX OQ'TTO RE YJ Patented Aug. 23, 1949 CONTROL MECHANISM FOR HONIN Y MACHINES Albert M. Johnson, Rockford, Ill., assignor to Barnes Drill 00., Rockford, 111., a corporation of Illinois Application December 4, 19M, Serial No. 566,485

13 Claims.

1 The invention relates to the art of finishing cylindrical holes or bores and more particularly to an improved machine for honing bores in relatively thin workpieces which provide bore walls ticahility of maintaining the reciprocatory m'ovements of the honing tool within the relatively close limits necessary to insure uniform tool action on the bore walls. In machines of the type referred to, the reciprocation of the tool is effeoted by reciprocating the carriage or head upon which the tool is supported.

One object of the invention is to overcome the above difficulties by providing an improved honmachine so constructed and arranged that the tool may be reciprocated in rapid, accurately controlled strokes while the head remains stationary thus permitting the reciprocatory movements of the head to be utilized solely for associating and disassociating the tool and work.

Another object is to provide a novel control system for honing machines adapted to efiect automatic operation of the machine through a cycle in which the tool supporting head is initially advanced to operatively associate the tool with the work, held stationary during the working portion of the cycle, and retracted at the end of the cycle to withdraw the tool from the work.

Still another object is to provide improved mechanism for reciprocating the honing tool through an accurately controlled working stroke substantially shorter than the length of the tool which mechanism is readily adjustable for working strokes of difierent length.

A further object is to provide simple, yet effective means for counterbalancing the weight of the tool spindle and tool so as to reduce the strain on the reciprocating mechanism.

Other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment illustrated in the accompanying drawings in which:

Figure l is a perspective view of a honing machine embodying the features of the invention.

Fig. is a transverse sectional view of the tool supporting head taken in a horizontal plane substa ntially on the line 2-4 of Fig. 1.

Fig. 3 is a sectional view of the head taken in a vertical plane substantially on the line 3--3 of Fig. 2.

Fig. 4:

is a sectional view taken in a vertical plane substantially on the line 4-4 of Fig. 3 showing the spindle reciprocating mechanism adjusted for minimum stroke.

Fig. 5 is a view similar to Fig. 4 but showing the reciprocating mechanismadjusted for maximum stroke.

Fig. 6 is a sectional view taken in a vertical plane substantially onthe line 6-43 of Fig. .3 showing details of the locking means for the reciprocating mechanism.

Fig. '7 is a diagrammatic view showing the electrical and hydraulic operating and control systems and their relationship to the mechanical elements of the machine.

For purposes of illustration, the invention has been shown and will be described herein as applied to a single spindle vertical honing machine of the type in which the honing tool is rotated and reciprocated relative to a stationarily supported workpiece. It will be understood, however, that the invention is not limited to use in a machine of the particular type illustrated and that various changes and adaptations may be made in the formgconstruction and arrangement of the parts without departing from the spirit and scope of the invention as defined by the appended claims.

Referring to Fig. 1 of the drawings, the machine selected to illustrate the invention comprises generally a bed or base ii! having mounted thereon an adjustable table or work support H and an upright column I2. The column I2 is located at the rear of the table and is provided on its front face with spaced parallel guide memhers it for supporting and guiding a reciprocatory tool head i4. Power driven means, herein shown as a pressure fluid operated actuator comprising a piston !5 (Fig. 7) working in a cylinder 55 and connected with the head by a rod I1, is provided for shifting the head toward or from the work support ii. A honing tool T (Figs. 1 and '7) of any suitable type is carried by a driver l8 attached in well known manner to the lower end of a rotatable spindle 2% supported in the head M.

In accordance with the present invention, support for the spindle 2!! is provided by an elongated tubular member or quill 2i fitted with anti-friction bearings constructed and arranged in well known manner to permit rotation of the spindle while preventing its endwise movement relative to the quill. The quill 21, in turn, is supported in spaced bearings 22 for limited endwise movement axially of the spindle. As the quill and spindle are constrained to move tosupported on the head it and having an adjustable eccentric connection with the quill 2i.

Referring to Figs. 2 and 3, the member 25, herein shown as a cylindrical bushing, is supported for rotation about its central axis by antifriction bearings 26 seated in a bearing sleeve 21 forming a part of a panel 28 rigid with the head 14. The panel 28 is arranged to overlie an opening 29 in one side wall of the head [4 so as to locate the rotational axis of the bushing substantially perpendicular to the axis of the quill 2i and is preferably'removably secured to the head as by machine screws 3E3- so that it may be removed therefrom along with the reciprocating mechanism as a unit. This unitary construction simplifies manufacture and assembly of the mechanism andfacilitates repair or replacement of worn parts.

The adjustable eccentric driving connection between the member 25 and the quill 2! is provided by a shaft 3| fitted in a longitudinal bore. 32 in the bushing and having at its inner end an eccentric crank pin 33 engaging in a transverse slot 36 formed in a cam block 35'rigid with the quill. In the exemplary machine, the cam block 35 is removably secured to a pad formed at one side of a cap member 36' rigid with the upper end of the quill. As will be seen by reference to Figs. 4 and 5-of the drawingsthe slot 34 in the cam lock is generallyoval and is dimensioned to receive the outer race ring ofan anti-friction bearing 31 mounted on the crank pin 33.

To provide adjustability, the bore 32 in the member 251s located eccentrically of the rotacrank pin 33. By rotating the shaft 3| in the bore 32, the axis of the crank pin 33 may be ad justed from the neutral or minimum stroke position shown in Fig, 4 inwhich it is alined with the axis of the member 25 to the maximum stroke position shown in Fig. 5 in which it is offset from the rotational axis of the member-by an amount equal to its eccentricity relative to the shaft 3| plus the eccentricity of the bore 32 relative to the axis of the member 25. With the mechanism adjusted for minimum stroke, the-machine maybe used for honing in the conventional manner.

Means is provided for locking the shaft 31 to the member 25 in various selected positions of adjustment. For this purpose, the shaft is formed with a peripheral flange Ali disposed inwardly of the crank pin 33 and adapted to extend over the adjacent end of the member 25. The inner face of the flangellfl is formed with a plurality of recesses arranged in. a circular row concentric with the axis of the shaft and suitably spaced apart circumferentially of the flange. These recesses are positioned to register with a detent eleh the member 25 by a'nut threaded on the shaft ably fixed to the shaft 3!.

4 3! serves to maintain the flange tightly engaged with the detent 42 thereby locking the shaft and member together for rotation as a unit about the axis of the member. Adjustment of the shaft to vary the eccentricity of the crank pin 33 may be conveniently effected by backing off the nut 45 and turning the shaft to the desired position. To provide a visual indication of the adjusted position of the crank pin, the washer 44 may be provided with a suitable index mark and non-rotat- As shown in Fig. 3, a set screw 46 threaded in the washer and engaging in a keyway 41 in the shaft prevents relative rotation of the parts.

While any suitable means may be utilized for driving the member 25 and the shaft 3|, it has been found especially convenient to drive this in a bearing sleeve 53 formed on the-panel 28 tional' axis of thebushing. Preferably, the eccen- .tricity of thebore is the same as that of the the quill 2!. The pinion 58 is formed with a wide face. so asto maintain its driving engagement with the gear 5'! asthe quill and spindle are reciprocated in the head.

As shown in Fig. 2, the. gears 59 and 5| are I located so that they are conveniently accessible for replacement whenever it is desired to change the driving ratio between the spindle and the reciprocating.mechanism. The gear 5| is held in place on the shaft 52 by a nut 59 threaded 0n the end 'of the shaft. The nut 45 and washer 44 perform a similar function for the gear 50. Preferably the gears and the retaining nuts are enclosed in a suitable housing Si removably secured to the outer face of the'panel 23.

Any suitable means ma be provided for driving the spindle 20. In the exemplary machine, the

spindle is adapted to be driven by a motor M stationarily supported on the column I Z and drivingly connected through a train of gears 6| with :a splined shaft 62 extending into the head I4 and parallel to its reciprocatory path. The shaft 62 has a splined driving connection with a gear 63 journaled in the head I 4 and meshing with a pinion 64 keyed to an intermediate shaft 65 journaled in the head. A gear 66 on the shaft 65 -meshes with the pinion 58 on the spindle, the wide "face of the pinion serving to maintain the driving connection as the spindle is reciprocated relative to the head.

Simple and eflicient' means is provided for counterbalancing the weight of the quill 2! and spindle 20 to relieve the strain on the reciprocating mechanism. The counterbalancing means in its preferred form, as shown in Figs. 3 and 7, comprises a compression spring 6? interposed between a rigid portion of the head and an arm 58 seaemczc went by. a wrenchwhereby the rod: may be screwed in or out to vary the spacing of the nut iron: the flange H and thus the tension of the spring.

In accordance with the present-invention, a control system of novel and advantageous characteris provided for eflectmgautomatic cycling of the machine in a manner which materially simplifies and reduces the work of the machine attendantan-d otherwise greatly facilitates the honing of shallow bores. 011cc the machine is set up for operating on a particular class of work, the attendants duties consist simply of placing the unfinished workpieces on the work; support, manipulating a single control element such asa push button to start the cycle, and removingth'e workpiece when the cycle is terminated automatically. v

For operating on work or which a typical example W is shown in '2' of the dr'awingeithe machine is provided with a honing tool or the proper grade and size for finishing the bore of such workpiece. In setting up the machine, suitable stops herein shown as sleeves t5 mounted on guide members it are rigidly secured in place thereon for engagement by the head Hi when the latter is shifted downwardly so as to substantially center the tool within the bore oi the workpiece. The eccentricity of the spindle reciprocating mechanism is adjusted in the manner above described to provide the required working stroke,

that is to traverse the tool axially of the work in a series of strokes such that the abrading elements of the tool are at all times in contact with the bore of the work throughout its entire length. A' timing device TD forming a part of the control system is set to determine the length of the working portion ofthe machine cycle. n a

Momentary actuation of a motor starting switch SI energizes a control; relay Rt which closes a switch RI I to complete a holding circuit for itself independently of the starting switch. This holding circuit may be interrupted to decriergizethe relay at any time by actuation 01' "a normally closed stop switch S2. Relay Rt, when 811818123861, 8180610588 a SWitGh Rlz t0 supply CHF- rent to a motor MI arranged to drive a pump? for supplying pressure fluid to the cylinder N5 of the head reciprocating actuator.

While the machine is idle, pressure fluid delivered by the pump P is by-passect to a reservoir or sump B through a normally open stop valve V. Upon closure of the stop valve, the pressure fluid supplied by the pump is directed by a reversing valve Vl to the upper or lower end. of

the cylinder It to advance or retract the piston I25 and the head 14' to which it is connected; A pilot valve V2 of the conventional rotary type controls the setting of the reversing valve in. well known manner thus determining the direction. in which the head is to be moved. 7

As shown in Fig. 7, the head 14 is in its upper or retracted position while the valves VI and V2 are set for directing the flow of pressure fluid to effect the advance of the head from such position toward the work support. It will be understood that the parts are positioned as shown in the drawing at the beginning of an operating cycle. In the retracted position of the head, the honing tool T is withdrawn a substantial distance above the workpiece W and into a guide fixture Tl which acts in well known manner to. maintain the tool in a contracted condition until:it has been entered in the work. Upon entering the work, the tool is expanded to force the abrasive elements against thewalls of the bore to be honed.

Arr operating cycle of the machine is initiated bymomentary closure of a normally open cycle starting switch S3 (Fig. 7) which oompletesan energizing circuit for a control relay R2. The relay uponenereizing. closes a switch Ell to start the spindle driving motor M and additionally closes a holding circuit for itself independent of the starting switch S3. The holding circuit, as

herein shown. includes an inching switchSl. a

limit switch LSi, acyclic stop switch S5 and the switches Rt t, R22 and S2. switch 15! is adapted to beheld open by a cam block: 18 or the like. when the head t4 is'tully retracted and to close uponmovement of the head away from the retracted position. A. selector switch Si is provided; so-tliatthe. holding circuit for the relay R2 may be placed under control of or rendered independent of the timing device TD selectively For purpose, a normally closed swatch TD! vance the head It toward the work support. Fuid from. the lower end of the cylinder H5 is exhausted through a resistance valve V3 and the valve VI to the sump R. Such downward movement-of the head continues until the head. engages the fixed stops 15 which have been positioned to internup-tthe movement of the head when the'tool is substantially centered in the workpiece W; A relietvalve V4 associated; with the pressure line fromrthe pump prevents excessive increase in pressure-"while the head. is maintained against the stops by thepressure of the fluid in the upper end of the cylinder Hi.

The head M is held in engagement with the stops; 15 while the tool '1 periorms its action on the workpiece. Tool action is effected through rotation of the tool by the motor M and simultaneous reciprocationby the reciprocating mechanism heretofore described. The timing of the tool action, conveniently called the working portion of the cycle, is ellected by the timing device TD which, alter a predetermined interval, opens the switch TDI and closes a switch TD2.

Opening of the switch TDI stops the spindle driving motor byinterruptingthe holding circuit .for the relay R2 in the event that the selector switch S6 has been appropriately set for such automatic stopping. With the switch S6 set in the position shown in the drawings, operation of the spindle driving motor continues until the head has been returned to retracted position as will appear presently. Closure of the switch TDZ completes anenergizing circuit for a solenoid S02 which shifts the pilot valve V2 to reverse position against the action of a spring 18 normally urging the valve to the advance position. Operation of the pilot valve initiates the shifting of the roversing valve VI to itsalternate position in which pressure fluid is directed to the lower end of the cylinder ,1 6 while the upper end of the cylinder is R2 and the circuits for the solenoids SCI and S02 areralso opened. Relay R2, upon deenergizing following the opening of the time switch TDI, stops the motor M and the timing device TD. Solenoid S02 permits the pilot valve to return to its normal rest position under the action of thespring 18'. -Solenoid 501 permits the stop valve V to return toopen position and thus render the'fluid pressure system temporarily inefiective. Preferably, the deenergization of the solenoids SO! and S02 is timed so that thereversing valve -VI maybe shifted to its head advancing position before the pressurefiuid system is-disabled. If for any reason,=this shift does not occur at-the end of the cycle, it will take place immediately upon the beginning of the succeeding cycle due to the setting ofthe pilot valve V2.

The retraction of the head [4 marks'the end of the machine cycleand the machine remains idle; until another cycle is initiated by"actuation :of the startingswitch S3. The retraction of the head advises the attendant that the-cycle has been-completed and he may remove the finished workpiece and replace it with another one tobe operatedJQn.

It will be apparent'from the foregoing that the invention provides a honingmachine embodying novel and advantageous features which particularly'adapt it for the honing of shallow bores and which greatly facilitate such operations. The novel cycle controlling. system incorporated in themach-ine materially simplifies and reduces the work of-the attendant so that a relatively unskilled workman may be placed in charge of the machine.

yThe inventionalso provides novel meansfor reciprocating the tool supporting spindle relative to the head for the performance of the honing operation thus permitting normal reciprocatory movements of the tool head to be utilized for associating and disassociating the tool and 'the work. The reciprocating mechanism is simple in construction, yet efiicient and reliable in operation. :iMoreover, it is readily adjustable through a wide range to adapt it for operation on a wide variety of work. a 1

I claim as my invention:

' 1. In a honing machine, a head mounted for reciprocation, a tool carrying spindle mounted on said head for reciprocation therewith and for reciprocation relative thereto, a support for work to be operated on by the tool carried by said spindle, a first power driven-means for reciprocating said-spindle, a second power driven means for advancing and retracting said head with respect to said work support, a control system including a manually actuated control element,

means in said control system operative in retion of said control element for initiating the operation of said second power driven means to effect an advance of said head to operatively asso- .ciate the tool with the work.

2. In a honing machine, a head mounted for .reciprocation, a tool carrying spindle mounted .on .said head for reciprocation therewith and for reciprocation relative thereto, a support for work to be operatedon by the tool carried by said spindle, a first power driven means for reciprocating said spindle, a second power. driven means for -.,fl. vancing and, retracting said head with respect to said work support, a control system including a manually'actuated control element, means in said control system .operative in response to a momentary actuation of said control element for initiating the operation of said first power driven means to effectthe reciprocation of said spindle and the tool carried thereby, other means responsive to the actuation of said controlelement for initiating the operation of said second power driven means to advance said head and operatively associate the tool with the work, and means fonoausing said second power driven means to retractsaid head and thereby disassociate the tool from the work after a predetermined interval.

1 3. In a honing machine, a head mounted for reciprocation, a tool carrying spindle mounted on said head for reciprocation therewith and for reciprocation relative thereto, a support for work to be operated on bythe tool carried by said spindle, a first power driven means for reciprocating said spindle, a second power driven means for advancing and retracting said head with respect tosaid work support, a control system including a manually actuated control element, means in said control system operative in response .to a momentary actuation of said control element for initiating the operation of said first power driven means to effect the reciprocation of said spindle and the tool carried thereby, othermeans responsive to the actuation of said controlelement for causing said second power driven means to advance said headso as to operatively associate the tool with the work and to hold said head in advanced position while; the tool is operating on the work, and timing means for causing said second power driven means to retract saidhead and disassociate the tool from the Work after a predetermined interval; :1 I 4. In a honing machine, in combination, a work support, a head mounted ior'movement toward and from the work support, a tool supporting spindle mounted on said head for rotation and for reciprocation relative thereto, a first power actuated means for advancing and retracting said head, a second power actuated means for reciprocating said spindle, control mechanism for the machine including a manually actuated element adapted when actuated to initiate the operation of both said power actuated means, said first mentioned power actuated means operating to advance said head to bring the tool carried by said spindle into operative association with work carried-on said work support, said second power actuated means operating to reciprocate said spindle and the tool while such operative association with the work is maintained, and a timing device started concurrently with said power actuated means operative to initiate the withdrawal of the head and thereby disassociate the tool from the work after a predetermined interval. '5. In a honing machine, a head mounted for reciprocation, a'tool carrying spindle mounted on said head for reciprocation therewith and for reciprocation relative thereto, a support for work to be operated on by the tool carried by said spindle,'a first power driven means for reciprocating said spindle, a second power driven means for advancing and retracting said head with respect to said work support, a control system including a manually actuated control element, means in said control system operative in response to a momentary actuationof said control element for initiating the operation of said first power drivenmeans to effect the reciprocation of said attests spindle and the tool carried thereby, other means responsive to the actuation of said'control ele= ment for causing saidfsecond power driven means to advance said head so as to operatively associate the tool with the work and to hold said head in advanced position while the tool isoperating on the work, timing means operative to interrupt the reciprocation of'said spindle by said first power driven means, and meanscontrolled by said timing means for causing said second power driven means to retract said head and thereby disasseciate the tool from the work.

6. In a honing machine, a head mounted for reciprocation, a tool carrying spindle mounted on said head for reciprocation therewithand for reciprocation relative thereto, a support for vv'ork to beoperated on by the tool carried by said spindle; a first power driven means for reciprocating said spindle, a second power driven means for advancing and retracting said head with respect to said work support, a'control system including a manually actuated control element, meats iii-said control system operative in response to a momentary actuation of said control element for initiating the operation of said first power driven means to effect the reciprocation of said spindle and the tool carriedthereby, other means responsive to the actuation of said control element for causing said second power driven means to advance said head so as to operatively associate the tool with the work and to hold said head in advanced position while the tool is operating on the work, a timer operative to cause said second power driven means to retract said head to disassociate the tool from the Work, control means actuated by said timer for interrupting the reciprocation of said spindle prior to the retraction of said head, and means operable selectively to render said control means operative or inoperative at will.

7. Spindle reciprocating mechanism for a honing machine comprising, in combination, a cylindrical member supported for rotation about a central axis and having a longitudinal bore located eccentrically of said axis, a shaft rotatably fitted in said bore, an eccentric crank pin at one end of said shaft, the eccentricity of said crank pin being adjustable relative to the rotational axis of said member by rotation of the shaft in said bore,

a peripheral flange adjacent one end of said shaft overlying the end of said member, said flange having a plurality of circumferentially spaced recesses, a detent element engageable selectively in said recess and in a complemental recess in said member to hold the shaft and member against relative rotation, and means detachably secured to the other end of said shaft and coacting with the adjacent end of said member to hold the shaft and member against relative endwise movement whereby to prevent disengagement of said detent means.

8. Spindle reciprocating mechanism for a honing machine comprising, in combination, a cylindrical member supported for rotation about a central axis and having a longitudinal bore located eccentrically of said axis, a shaft rotatably fitted in said bore, an eccentric crank pin at one end of said shaft, the eccentricity of said crank pin being adjustable relative to the rotational axis of said member by rotation of the shaft in said bore, a peripheral flange on said shaft extending over the adjacent end of said member, a plurality of recesses in said flange spaced apart circumferentially of said shaft, a recess in the adjacent end of said member, and a detent element seated s in the recess in said member and engageable selectively in the recesses in said flange to hold said shaftagainst' rotation relative to said member.

9. In a honing machine, in combination, a nonrotatable axially reciprocable quill having a tool supporting spindle journ'aled therein, means for reciprocating said quill comprising a shaft disposed with its axis substantially perpendicular to said 'q'uiil, an eccentric crank pin at one end of said shaft operatively connected with said quill, a'rot'atably supported bushing having a' longitudiiialbore for the reception of said shaft, said here being located eccentrijcally with respect to the rhtati'ohal axis of said bushing whereby the eccentricity of said crank pin may be adjusted with respect to said axis by turning said shaft reacts to said bushing, means for locking said shaft'a'nd said bushing together in any selected position of adjustment, and means for driving said bushing.

4 10. In a'honing machine, in combination, a re ciproc'atory head, an elongated tubular member supported in said head for limited endwise movemecca tool supporting spindle journaled in said member and secured against endwise movement relative thereto, power actuated means for re ciprocating said head, power actuated means for rotating said spindle, ajrotatable member supported on said head with its axis substantially F perpendicular to the longitudinal axis of said tubular member, an eccentrically disposed crank pin rotatable with said last mentioned member and coacting with said tubular member to reciprocate the tubular member and said spindle in response to such rotation, and means providing a driving connection from said spindle rotating means to said rotatable member.

11. In a honing machine, in combination, a head supported for reciprocation, a tool carrying spindle mounted on said head for reciprocation therewith and for rotation and reciprocation relative thereto, a support for work to be operated on by the tool carried by said spindle, a motor for rotating and reciprocating said spindle, pressure fluid operated means for advancing and retracting said head with respect to said work support, a control system for the machine including a manually operable starting switch, a relay adapted to be energized in response to the actuation of said starting switch, a first switch closed by said relay when energized to initiate the operation of said motor, a second switch closed by said relay when energized for initiating the operation of said pressure fluid operated means to advance said head and operatively associate the tool with the work, an electrically driven timing device started in operation concurrently with the energization of said relay, and means including a switch actuated by said timing device for initiating reverse operation of said pressure fluid operated means to retract said head and thereby disassociate the tool from the work.

12. In a honing machine, in combination, a head supported for reciprocation, a tool carrying spindle mounted on said head for reciprocation therewith and for rotation and reciprocation relative thereto, a support for work to be operated on by the tool carried by said spindle, a motor for rotating and reciprocating said spindle, pressure fluid operated means for advancing and retracting said head with respect to said work support, a control system for the machine including a manually operable starting switch, a relay adapted to be energized in response to the actuation of said starting switch, a first switch closed by said, relay whenenergized to initiate the opera,- tion of said motor, a second switch closed by said relay when energized for initiatingthe operation. of said pressure fluid operated meansto advance said head and operatively associate the tool with the work, stop means for interrupting the advance of said head to maintain the tool in operative relation with the work, an electrically driven timing device, means including a switch operated byfisaid timing device for initiating reverse operation of said pressure fluid operated means to retract said head and thereby disasseciate the tool from the work, and means operative upon the retraction of the head for stopping said timing device and said pressure fluid operated means. I I p 13. In a honing machine, in combination, a head mounted for lineartranslation, a tool carrying spindle mounted on said head for translation therewith and for reciprocation relative thereto, a support for work to be operated on'by a tool carried by said spindle, power driven means for reciprocating said spindle, pressure fluid actuated means for advancing and retracting said head with respect to said work support, a manually actuated control element, and control means including a valve and a timing device operative in response to a momentary actuation of said control element for initiating the advance of said head by said pressure fluid actuated means REFERENCES CITED The following references are of record in the file of this patent: l

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